My first thought was fossilized dinosaur poop. No joke, its a real thing and can be found out west. It probably is not, but Im sure someone else here will know what it is.
After looking it up, it could be fossilized poop for sure. Apparently there is some major paleontology site in the Fort Dodge area. See here Dinosaurs in Iowa ? Iowa Geological Survey
Some more people will respond eventually. In any case, its probably not a dinosaur fossil, but it does look like it could be to me. I am no expert on stone or anything. It also looks like it could have came out of a cave to me.
In my professional opinion I recognize that as the droppings of an oversized Mastadon due to the rippling of the sample. The bioscopic density of this specimen, is most intriguing. I would package this very carefully and take it straight to the curator of the nearest Museum!!!!